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Dry Curing and Fermentation

nepas provided this very important and in depth information about dry curing and fermentation as written by Robert E. Rust

Historical
Dry and semi-dry sausage represents one of the oldest forms of meat preservation. Without knowing why our ancestors found out several thousand years ago that salted meat, either in whole pieces or cut up and stuffed in animal casings, would keep for months under normal climatic conditions when properly dried. Certain areas of Europe, particulary Northern Italy, Switzerland, and Hungary, because of their ideal climatic conditions, developed reputations for the production of these sausages which were dried, either in caves or in sheds.

It wasn't until 1900 that the microbial basis for dry and semi-dry sausage production was first discovered. In 1940 the first patent covering the use of a starter culture to prepare semi-dry sausage was issued. In 1958 the first commercial starter culture was offered to the meat industry.

European vs. US Type Products
As the dry and semi-dry sausages moved to the US from European origins, several changes took place. In Europe, fermentation is usually a slow process with fermentation temperatures around 75°F(24°C). Subsequent drying is also at low temperatures. European type products are seldom heat treated.

In general, many European type sausages tend to be less dry than their U.S. counter-parts. In Europe, you would expect a semi-dry sausage to lose 15% of its weight during drying and a dry sausage to lose 30% of its original weight. In Europe the product standards are characterized based on water activity (Aw) as opposed to moisture: protein (M:P) ratios.

Another difference is final pH. The U.S. market expects pH's to be relatively low. Dry salamis will generally have a pH of 5.0 to 5.4. Some of the semi-dry products like "summer sausage" may have a pH of 4.5 to 4.7, considerably lower than the European market would tolerate

Characteristics
Dry and semi-dry sausage differ from all other types of sausage in that they require microbial fermentation. This fermentation reduces the pH of the product to 5.0 to 5.3 for dry sausage and 4.6 to 5.2 in the case of semi-dry sausage. In addition, some of the moisture is removed by drying to produce a relatively low Water Activity (Aw) of approximately 0.85 in the case of dry sausage and 0.85 to 0.91 in the case of semi-dry sausage. The combined low pH plus the reduced Aw present conditions that contribute to the extended shelf life of the product. Table 1 shows the Moisture Protein Ratios (MPR) that the USDA requires for various products. It should be pointed out that in the U.S. we base the degree of drying on MPR as opposed to Europe where Aw is used.

Product

Ratio

Jerky

0.75:1

Pepperoni, Chorizo in Lard

1.6:1

Salami, Dry Salami, Turkey Salami

1.9:1

Genoa Salami, Sicilian Salami

2.3:1

Thuringer Cervelat or other Semi Dry Saus w/ Lactic Acid Culture

3.7:1

Early sausage makers depended on fermentation by indigenous microorganisms that were present on the meat ingredients, the spices or the environment. From this evolved the "backslop" method of inoculation which depended on taking the meat batter from a previous batch and using it as a "starter". A variation of this was the maintenance of a "mother batch" from which the starter was derived. All these methods involved the chance of introducing unwanted spoilage organisms along with the desirable bacteria. It wasn't until the 1950's that specific starter cultures were introduced.

In order to insure appropriate fermentation it is essential that starter cultures be used. There are two types of dry and semi-dry sausage producers who do not use starter cultures-those who have had product failures and those who are going to have product failures.

Raw Materials
Because of the critical nature of dry and semi-dry sausage production, only the highest quality meat ingredients should be used. The reason for this is that the product will be held at ideal temperatures for microbial growth for extended periods of time. Even with starter cultures, heavy microbial loads on the meat raw material could result in the growth of undesirable organisms with the production of off flavors, colors, textures and even product spoilage.

Some of the problems related to spoilage are "greening", a bleaching effect on the lean resulting in a white sausage that appears to be mostly fat, development of a mushy texture due to proteolysis, and an oiling out of the fat due to lypolysis. The greening problem results from peroxides produced by bacteria growing in the meat usually prior to processing. These organisms are fairly heat resistant but could be killed during heat treatment. They do, however leave behind the byproducts of their growth, namely peroxides which cause a greening of the pigment when exposed to air.

In traditional processing, dry and semi-dry sausage will often not be subjected to cooking temperatures during the process. This means that you would have little or no control over the final microbial loads. For the most part, these sausages will also be eaten without further cooking so that any microbial growth that occurs during production will be transferred to the ultimate consumer.

Because of microbiological concerns, particularly E coli 0157:H7, Salmonellea, and Listeriamonocytogenese all U.S. products will probably need to be heat treated. Producers of dry and semi-dry sausage are now required to validate the effectiveness of their processes in the destruction of E coli 0157:H7. It appears that in order to achieve appropriate destruction of this organism, heat treatment is probably the only alternative. This will drastically effect the texture and character of U.S. type dry sausages.

Trichina control in pork products is of less importance today but the regulations still exist.

Freshness is critical in the manufacturing dry and semi-dry sausage. Fats begin to oxidize immediately after slaughter. While the total oxidation and the development of rancidity takes a relatively long time even the slightest degree of rancidity will eventually trigger the rapid onset of rancidity in the finished product. For this reason, long storage periods in either a fresh or frozen condition should be avoided.

The pH of raw materials is also critical. Actually, we would like to work with meat raw materials that have the lowest possible pH because the ultimate goal of the fermentation is to reduce pH. For this reason, dark firm and dry pork (DFD) or dark cutting beef should be avoided. PSE pork should also be avoided since the protein is damaged to the extent that color and texture will be negatively effected.

Color of lean and fat are also important for visual appearance. Meat with yellow or soft fat would be acceptable in emulsion type sausage but not in dry and semi-dry sausages. The more intensely pigmented lean meat is also preferred. For this reason we would opt for pork shoulder meat as opposed to paler ham and loin trimmings.

In these sausages we usually don't apply sufficient cooking to hydrolyze the collagen into gelatin. For this reason we like to avoid meat with a high amount of connective tissue. Some processors actually use desiniewing, either by machine or by hand, to remove connective tissue.

An advatage of low pH in the fermented product, other than the preservative and flavor effects, is the fact that it promotes more effective drying. The closer the meat is to the isoelectric point, the more rapidly it will lose moisture. Meat with salt added will reach its isoelectric point at a pH of approximately 4.6 to 4.8. The closer to that pH, the more we facilitate the loss of moisture from the product as it dries.

Temperature of raw materials is also critical. For the most part, chopping or grinding of lean meats produces better particle distinction at temperatures of 24°F to 26°F (-4°C to 5°C). Actually if fat meats and fat are frozen to a temperature of 5°F to 10°F (-15°C to -12°C). They will produce better particle distinction as well. It is imerative that temperatures be maintained as low as possible to reduce fat smearing during stuffing. Smeared fat reduces the effectiveness of moisture loss and can result in product failure due to inadequate or uneven drying. Fat smearing may also interfere with microbial fermentation of the product.

In addition, temperatures above 40°F(4°C) during mixing can promote fat loss during cooking in those dry or semi-dry sausages that are heated to temperatures of 140°F (60°C) or above.

Chopping and Mixing
There are two schools of thought regarding particle reduction in dry and semi-dry sausage. Many people like to use a chopper since the knife action promotes more clean cut particles. The disadvantage of the chopper is the fact that it is difficult to produce uniform particles from one batch to the next and the chopper does not provide any opportunity for the use of a bone removal system.

The grinder on the other hand, will produce uniform particles but unless temperatures are carefully maintained and unless the equipment is maintained in topnotch condition, it is easier to develop fat smearing and lack of particle distinction. The grinder does have a distinct advantage in that it can be fitted with a bone removal system on the final grind. Some processors will do the initial cutting in the chopper and then finish the product through a grinder to produce the uniform particle size.

In order to maintain good particle distinction and reduce fat smearing, it is preferable to go through a final grind before the meat is blended with the non-meat ingredients. After salt is added to meat, the protein extraction that results will cause the mixture to become quite sticky and reduce the effectiveness of the grinding process.

In order of addition of non-meat ingredients to the mixer is also critical. Salt should be added toward the end of the mixing contrary to the normal procedure which we would use in the production of an emulsion type sausage where we encourage protein solublization and extraction. The addition of starter culture should be made after the curing ingredients are thoroughly dispersed. Actually, the only purpose of mixing is to uniformly disperse the spice, salt, cure and other ingredients. Over mixing should be avoided at all costs and a good sign of over mixing is the accumulation of fat on the mixer paddle surfaces.

A paddle mixer or blender is preferable to a ribbon type blender. Many processors will use a vaccum mixer to remove air from the mixture and produce a more dense product with superior visual qualities as well as superior keeping qualities because the air incorporated into the mixture is reduced.

If chilling of the meat is necessary, dry ice is preferable to wet ice since in a dry or semi-dry sausage we are trying to lose moisture rather than add additional moisture. It may be necessary during the grinding steps to rechill the meat if it is not sufficiently cold to produce good particle distinction. During the grinding process it is common to use a coarse grind to initially promote uniform distribution of fat followed by a second or final grind. The final grinding step will often call for a finer grind, say 1/8 inch for the lean meat with a 3/16 inch grind for the fatter meats. This system likewise reduces the possibility of smearing.

Non-meat Ingredients
Salt, sodium nitrite and seasonings are basic. Sugar is a source of energy for the fermenting microorganisms such as dextrose. Dextrose is actually the most universally used fermentable sugar although there are some organisms that can ferment sucrose or lactose. The amount of the dextrose added should be appropriate for the fermentation desired. Generally the higher the level of dextrose, the greater the degree of fermentation and the lower the final pH. For many dry sausages, eight to twelve ounces of dextrose per hundred pounds is sufficient. Twelve to sixteen ounces per hundred pounds is characteristic for semi-dry sausages and, for a highly fermented product like Lebanon bologna, one to two pounds are often added.

Today most processors use sodium nitrite as the source of cure. On some dry sausages, nitrate is still included. From a technical standpoint, however, there is relatively little advantage to using nitrate over nitrite.

It is also common for some processors to add an antioxident to dry sausage. This may change the flavor profile somewhat since on some of our dry sausages, which require longer drying periods, the rancid flavor may actually contribute to the overall flavor profile of the sausage.

As stated previously, starter cultures are highly recommended for uniformity and to insure that the pH drop will be rapid enough to inhibit the growth of undesirable organisms. Generally, the low temperature cultures, that is those that grow best at temperatures of 70°F to 80°F (21-27°C) may give the most preferred flavors, but these do require longer fermentation times. The higher temperature cultures are faster and the flavor is completely acceptable, particularly for the more highly spiced and seasoned sausages. Normally, the low temperature fermenting cultures are used for the dry sausages with the higher temperature fermenting sausages being used for snack sticks and the semi-dry sausages.

There are two types of cultures available. One is the freeze-dried culture and the other the frozen culture. Each of these cultures require special handling and you should consult the culture manufacturer for the appropriate procedure. They are normally stored in a freezer, and being living organisims have limited storage life. Both cultures require reconstitution in water. Heavily chlorinated water can adversely affect the cultures. Using hot water to thaw frozen cultures can likewise destroy the cultures.

Different culture manufactures produce cultures using a variety of lactic acid organisms. From my experience, the cultures produced in the United States are far superior in performance to those produced in some European countries. Many of the cultures used in European countries tend to react quite slowly and by nature will not ferment to sufficiently low pH's to satisfy the U.S. tastes.

Some processors use chemical acidulants, such as GDL (glucono delta lactone) or encapsulated lactic acid. The problem with these acidulants is that normally they cannot be used in sufficient quantity to get the low pH's we expect from our fermented products and they tend to have a somewhat harsh flavor. If you are using GDL, it is important that the product be stuffed immediately after the GDL is added and then moved into heat processing without delay. When encapsulated acid is used, the product must be heated to a temperature that will release the acid.

Because we depend on very long processing times, natural spices appear to function better from the standpoint of flavor stability than the spice extractives or oleoresins. It is important, however, that these natural spices be treated to reduce bacteria and mold counts.

We sometimes apply mold inhibitors on the casings. It is also possible to apply mold inhibitors to the product after stuffing. Smoking the product will retard mold growth.

While on the subject of mold, there are some traditional dry sausages that actually depend on surface mold growth to achieve their unique characteristics. There are mold cultures available to inoculate the surface although many producers simply inoculate the new batch from a previous lot. This is done just prior to entering the drying room. The desirable molds for this purpose should produce a white mycelium with no black or other colored fruiting bodies. Undesirable molds produce variable colored fruiting bodies and nay even attack the casings and cause disintegration of the casings.

Stuffing
It is essential that the proper casing be used for the product. Depending on the type of product, natural, collagen or cellulose casings could be used. There are some excellent fancy casings which are made from silk reinforced collagen. These casings are extremely thin and have good drying rates. There are even some novelty casings made from sewn collagen, fibrous, or natural casing material. These can range in shape from footballs to little pigs.

If you are using natural casings, make sure they are in good condition. Some of the large diameter natural casings, such as double walled sewed bungs, if they are stored too long or improperly stored, will develop rancidity of the adhering fat. This rancidity will carry through into the product so good quality control measures should be used in selecting the casings.

It is essential that casings be stuffed to the proper diameter. Understuffing can result in air pockets developing between the casing and the sausage as the sausage dries and shrinks. Overstuffing can result in ruptured casings or clips being forced off the end of the casings as the meat expands during the initial phases of the fermentation cycle.

For dry sausages such as pepperoni that will be pealed before slicing, there are some very specific requirements. Essentially the fibrous casing needs to have close adherence to the surface during the fermentation and heat treatment stages. If the casing loosens at this point, surface fat pockets can develop. Subsequently, the casing needs to loosen so it can be easily stripped off prior to slicing.

To avoid smear, you need to use stuffing horns that are in good condition and free of nicks and dents and as large as possible. Likewise, the stuffing horn and transfer pipe should be as short as possible. Stuffing pressure should be limited to an amount sufficient to dispense the meat at the appropriate stuffing rate. Be sure the stuffing valves are fully open if you are using a piston stuffer since a partially closed valve will contribute substantially to smear.

Fermentation
If the meat is extremely cold, when it is stuffed into the casings, there will be a tendency toward moisture condensation on the surface of the casing immediately after stuffing. If this excessive condensation is allowed to carry through into the green room, the surface growth of microorganisms could cause problems in color or flavor.

The goal of the fermentation stage is to provide optimum conditions of temperature, humidity and time for the lactic acid producing bacteria to grow, produce lactic acid and other metabolic products and also overgrow any undesirable organisms, either those which cause food spoilage or the pathogenic organisms. The conditions need to be favorable to the starter culture and you should follow the culture supplier's recommendations.

Generally for semi-dry sausage, the fermentation temperatures would be in the range of 80°F to 110°F (27-43°C) with a 95% relative humidity. Under these conditions a good starter culture should achieve full fermentation in less than 24 hours.

For dry sausage, where fermentation is conducted at a lower temperature of 75°F to 80°F (24-27°C), it may take as long as 48 hours to achieve appropriate fermentation.

It is important to bring up the temperature slowly in the initial stages of the fermentation to avoid undue condensationon the surface of the product when the cold product is transferred into a warmer area. Humidity control during fermentation is also critical since too low a humidity can reduce the growth of the lactic acid organisms, particularly at the surface.

Following the fermentation, the product may be smoked. It is preferable to apply smoke after fermentation is complete and surface color has developed. Other than monitoring the pH of the sausage, a good indication of complete fermentation is a firming of the product. As lactic acid is produced it denatures the protein much in the same manner as protein is denatured by cooking and the product becomes firm. Along with this, the desirable cured color develops.

Once fermentation is complete, the drying cycle can be commenced. In fact, some people may lower humidity at the end of the fermentation cycle to achieve an initial moisture loss of about 10 to 12% by weight.

Drying
The drying of dry sausage is a very critical step. It is a situation where moisture and air circulation are balanced to remove moisture from the surface of the sausage at about the same rate as is transferred from the interior. In general, drying rates in excess of about 1 percent a day weight loss will result in case hardening. Once case hardening occurs the moisture loss from the surface is essentially suspended. The net result is that the product will develop deep creases and often voids in the interior as it begins to shrink.

The drying room temperature are normally maintained some where in the range of 60 to 65°F (15-18°C). A good rule of thumb is to start with a relative humidity that is no more than 5% below the water activity of the sausage. Thus, if you place a sausage in the dry room with a water cativity of 0.90 you would maintain a drying room humidity of 85%. As the product loses moisture and the water activity decreases you can then decrease the relative humidity of the drying room accordingly.

Below is an example of a typical temperature and humidity cycle for a high quality dry sausage. To monitor the correct degree of shrinkage, you can either monitor the water activity of the product or determine periodic moisture protein ratios until either the desired Aw or moisture protein ratio is achieved.

EXAMPLE 1

Time

Temperature

RH

1st Day

72-75°F

94-96%

2nd Day

68-72°F

90-92%

3rd Day

65-68°F

85-88%

If necessary continue until fully cured

68°F

85%

Possible variation: Start with 68-75°F, no humidity added, until surface moisture is driven off but without drying casing. Then continue according to above schedule.

Time

Temperature

RH

3-4 Days

65-72°F

92-95%

After 8-12 hours add very light smoke INTERMITTENTLY until color is set; then add more smoke. Semi-dry sausages can be processed according to these two schedules and if schedule A is used, then smoking is carried out at the completion of Schedule A according to the following:

Time

Temperature

RH

Smoking after curing, pre drying, desired color/flavor

60-65°F

75-85%

Exact RH depends on stage to which product was pre-dried.

EXAMPLE 2

If a high-quality product with higher moisture loss is desired, then the processing according to the following schedule is suggested:

Time

Temperature

RH

Maintain this temperature until product is fully cured

60-65°F

90-95% After 3-4 days reduce to approx. 85-90%

At the end of the pre-drying period, the product can be smoked if so desired, and then transferred to the drying room or, in the case of air-dried products, the product is transferred immediately to the drying room until the desired degree of moisture loss is obtained.

Time

Temperature

RH

Drying room until desired shrink is reached

60-65°F

75-80%

Scheneider, 1984

Packaging
Once the dry or semi-dry sausage has reached its proper pH and moisture protein ratio or Aw it is ready then for packaging and distribution. Vacuum packaging is very successful, however, at times you will find the accumulation of moisture inside the vacuum package and the result may be either an unsightly casing surface or possibly some deterioration of the surface of the sausage. For this reason, dry sausage is often packaged in a gas flush atmosphere. Of course, where the sausage is presliced, such as the case of presliced pepperoni for pizza, the use of a gas flush package is almost an imperative. The gas of preference would be and inert gas, usually nitrogen. It is important to flush all of the oxygen from the package before replacing it with the inert gas.

One technique that is used in Europe for the storage of large quantities of dry sausage is to place it in a master container with a nitrogen atmosphere. When the product is ready to be released for distribution, it is then given a brief smoking to "refresh" it. The net result is that the product can be stored for several months and then placed in the distribution stream without any noticeable deterioration in quality.